Released on the 15th of June 1768, the first 4 Mon coins had "Kanei Tsuho" on the obverse and 21 waves
(or Nami, in Japanese) on the reverse. Produced at the Kameido (or Fukagawa, depending on the source of information)
mint in Edo, Musashi provice, these coins were made of brass and contained a 68:24:8 ratio
of copper to zinc to tin. In 1769, the reverse design was changed from 21 waves to the more widely recognized
11 waves pattern. The production of these coins at the Kameido mint ceased in 1788, after which 157,425,360
coins had been produced. However, several other mints later commenced creating 4 Mon, albeit with
different alloys (which also gave them a different color, making them easy to tell apart).
First produced in 1860, iron 4 Mon were shiny when they were first cast.
However, most examples today have become rusty with age. Also, the Japanese citizens
did not like to exchange their copper coins for them, as they did not value iron as highly
as they did copper. These coins often have mint marks on the back, making them easy to identify.
As with the copper 4 Mon, they generally have 11 waves on the back
(some 21 wave examples exist, but these are scarce).